Concerned that the agency operating LAX could be illegally sending money to the city of Los Angeles, two Southern California congressmen are calling for a more thorough investigation and audit of Los Angeles World Airports' spending patterns.

Reps. Gary G. Miller, R-Rancho Cucamonga, and Howard P. "Buck" McKeon, R-Santa Clarita, want the Department of Transportation's inspector general to raise the profile of an ongoing investigation into LAWA's spending practices. Federal law prohibits airports, which are funded largely through federal grants and airline fees, from helping to fund municipal governments.

Miller and McKeon wrote a letter to Rep. Tom Latham, R-Iowa, chairman of the House Subcommittee on Transportation, Housing and Urban Development, and Related Agencies. The two asked Latham to consider adding "strong language" in the next transportation appropriations bill to warn airport managers like Los Angeles World Airports to be careful about so-called revenue diversion. They also asked Latham to look into allegations regarding a possible lack of thoroughness in the current audit, which began in 2012.

"We ... have been reliably advised that during the course of their official duties, two senior investigators were removed from this investigation after requesting documentation on the exorbitant and disproportionate costs and lack of reimbursements for contracted policing services at LAWA," Miller and McKeon wrote. "Since there have been so many irregularities in this process, we would ask that you seek a forensic audit to determine the extent of the diversion of federal funds at LAWA."

The letter, dated March 12, comes as the union representing airport police officers continues to pressure airport executives for better working conditions, including improved police cars and a new police station. The union has accused airport executives of not providing improvements as quickly as promised.

The police union has long contended that the airport spends too much money contracting with the Los Angeles Police Department and not enough on the airports police division, which is responsible for security at LAX, Ontario and Van Nuys Airports.

Police union leaders say some of the LAPD officers are unnecessary, and that they are sometimes used as a way to move money from the airport into city coffers in violation of federal law. A 2012 audit by the Federal Aviation Administration cleared the airport of allegations of improperly using funds for police, but found that the airport had kept poor records.

In their letter, the two congressman called that FAA audit "contradictory and inconclusive" and urge further probing into the issue of police funds.

Arif Alikhan, deputy executive director for law enforcement and homeland security for Los Angeles World Airports, said airport officials were aware of the letter and will continue to comply with all audits and investigations.

"When we are asked to provide information, we are doing it without hesitation," he said.